"Select All" option for two or more dropdown list

Question

I have two drop-down list in which one is "State" and another is "Cluster". Both of these drop-down list are relational. For example if I select Kerala in State then Cluster will populate its important cities and dist. like Pathnamthitta, calicut, palakad etc.

So, what I want is, I want to give an option "Select All" in both State and Cluster ddl.

I've gone through:

How to select all records in a DropDownList

http://www.w3schools.com/aspnet/control_dropdownlist.asp

http://forums.asp.net/t/1221977.aspx?Adding+a+Select+all+option+to+a+drop+down+list

But none of them worked for me. I can able to have select all in state but not getting cluster values populated on the other ddl.

This is my code for "State" ddl:

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
DataSet3TableAdapters.tbl_energy_reportTableAdapter state;
state = new DataSet3TableAdapters.tbl_energy_reportTableAdapter();
DataTable dt = new DataTable();
dt = state.GetDataByStateInnerJoin();
DropDownList1.DataSource = dt;
DropDownList1.DataTextField = "state1";
DropDownList1.DataValueField = "state1";
DropDownList1.DataBind();                
DropDownList1.Items.Insert(0, new System.Web.UI.WebControls.ListItem("--Select State--", "0"));
DropDownList2.Items.Insert(0, new System.Web.UI.WebControls.ListItem("--Select Cluster--", "0"));
}
}

And This code is for "Cluster"

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{

DataSet3TableAdapters.tbl_energy_reportTableAdapter state;
state = new DataSet3TableAdapters.tbl_energy_reportTableAdapter();
DataTable dt = new DataTable();
dt = state.GetDataByClusterInnerJoin(DropDownList1.SelectedValue);
DropDownList2.DataSource = dt;
DropDownList2.DataTextField = "cluster";
DropDownList2.DataValueField = "cluster";
DropDownList2.DataBind();

}

This is the query for State ddl:

SELECT DISTINCT tbl_site_details.state1
FROM            tbl_site_details INNER JOIN
                         tbl_energy_report ON tbl_energy_report.Site_ID = tbl_site_details.site_id

And this the query for Cluster ddl:

SELECT        tbl_site_details.cluster
FROM            tbl_site_details INNER JOIN
                         tbl_energy_report ON tbl_energy_report.Site_ID = tbl_site_details.site_id
WHERE        (tbl_site_details.state1 = @state1)

Answer 1

That's because rebind the ddl2 with dt on ddl1_selectedindexchanged method.

Comment the 'DropDownList2.Items.Insert' on your page_load

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
DataSet3TableAdapters.tbl_energy_reportTableAdapter state;
state = new DataSet3TableAdapters.tbl_energy_reportTableAdapter();
DataTable dt = new DataTable();
dt = state.GetDataByStateInnerJoin();
DropDownList1.DataSource = dt;
DropDownList1.DataTextField = "state1";
DropDownList1.DataValueField = "state1";
DropDownList1.DataBind();                
DropDownList1.Items.Insert(0, new System.Web.UI.WebControls.ListItem("--Select State--", "0"));
//COMMENT THIS LINE
//DropDownList2.Items.Insert(0, new System.Web.UI.WebControls.ListItem("--Select Cluster--", "0"));
}
}

and move it to your dropdownlist1_selectedindexchanged event.

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{

DataSet3TableAdapters.tbl_energy_reportTableAdapter state;
state = new DataSet3TableAdapters.tbl_energy_reportTableAdapter();
DataTable dt = new DataTable();
dt = state.GetDataByClusterInnerJoin(DropDownList1.SelectedValue);
DropDownList2.DataSource = dt;
DropDownList2.DataTextField = "cluster";
DropDownList2.DataValueField = "cluster";
DropDownList2.DataBind();

//put it here
DropDownList2.Items.Insert(0, new System.Web.UI.WebControls.ListItem("--Select Cluster--", "0"));
}